Field of the Invention
The present invention relates to an air flow sensor and an optional device that is for an electrical machine and that includes the air flow sensor.
Discussion of the Background
Electrical machines such as image forming apparatuses emit exhaust gases that contain ultrafine particles (UFPs) of siloxane, which results from heating of silicon, or hydrocarbon, which results from melting of toner at high temperatures. In recent years, stricter regulations have been imposed on ultrafine particles. This requires the electrical machines to use a filter or a similar device to collect ultrafine particles in the exhaust gas and to discharge purified air to the atmosphere. Newly developed electrical machines are designed to satisfy this requirement against ultrafine particles in the exhaust gas. In order for existing electrical machines to satisfy the requirement, a discrete, optional device that has a function to purify the exhaust gas may be added to the existing electrical machines.
When an optional device is discretely mounted to an electrical machine such as an image forming apparatus, the optional device can be powered directly by a commercial power source. It is necessary, however, to electrically connect the electrical machine and the optional device to each other in order for the electrical machine to send the optional device electrical signals to control operation of the optional device.
For example, while the image forming apparatus is in waiting mode, an exhaust gas fan is out of operation or rotating at speeds so low that the amount of exhaust gas is negligibly small. Thus, the amount of ultrafine particles in the exhaust gas is negligible. While the image formation unit is in operating mode, the exhaust gas fan is rotating at full speed, emitting a larger amount of exhaust gas, which contains a larger amount of ultrafine particles. This necessitates control that includes sending the optional device an electrical signal to determine whether the image forming apparatus is in waiting mode or operating mode and making the optional device effect its air purification function while the image forming apparatus is in operating mode.
In order to implement the electrical connection between the electrical machine and the optional device, it is necessary to provide, in advance, the electrical machine with an interface (such as a connector) to make the electrical connection with the optional device possible. Providing the interface leads to an increase in cost. For an existing electrical machine without such interface, it is necessary to modify the electrical machine so as to retrieve the electrical signal and implement the electrical connection with the optional device.
In view of this situation, the inventors worked on the development of an optional device that has an air purification function and that can be discretely mountable to electrical machines while eliminating the need for electrical connection. This optional device includes an air flow sensor and a controller, The air flow sensor detects exhaust gas from the electrical machine. The controller controls the operation of the air purification function (the operation of an electric fan) based on a detection signal from the air flow sensor. That is, the optional device determines how the electrical machine is operating by detecting the exhaust gas from the electrical machine, instead of by receiving an electrical signal from the electrical machine. This enables the optional device to turn the air purification function into operation at any desirable time.
Japanese Unexamined Patent Application Publication No. 1-146519 discloses a differential pressure sensor similar to the above-described air flow sensor. The differential pressure sensor is for a vacuum cleaner. The differential pressure sensor includes a slider and a variable resistor. The slider is fitted in a cylindrical case and movable in an axis direction of the cylindrical case. The variable resistor includes a movable contactor that is movable together with the slider. When the slider is moved due to a difference between the pressure in an intake air flow path of the vacuum cleaner and the atmospheric pressure, the differential pressure sensor regards the movement of the slider as a change in resistance value of the variable resistor.
In the differential pressure sensor, it is necessary that the slider be in contact (airtight contact) with the inner surface of the cylindrical case while making a sliding movement. The necessity of contact requires high levels of accuracy in the process of making the slider and the cylindrical case. If the accuracy of the process is less than the required accuracy, it may be difficult or impossible to ensure optimum operation of the differential pressure sensor. In contrast, not as much accuracy is required of air flow sensors dedicated to detecting exhaust gas from image forming apparatuses; rather, a simple configuration costing as low as possible is preferred.
Additionally, in the above-described differential pressure sensor, a load occurs by the interfacial friction between the slider and the inner surface of the cylindrical case involved in the movement (sliding movement) of the slider. This makes the differential pressure sensor suitable for detecting air of comparatively greater force such as suction force from a vacuum cleaner and wind force from an electric blower. The differential pressure sensor, however, is difficult to use as an air flow sensor to detect air of comparatively weaker force such as the force of exhaust gas from an image forming apparatus.
It is an object of the present invention to provide an air flow sensor that deals with the above-described circumstances and to provide an optional device that is for an electrical machine and that includes the air flow sensor. Specifically, the air flow sensor has a simple configuration costing as low as possible and is suitable for detecting air (air flow) of comparatively weaker force such as the force of exhaust gas from an image forming apparatus.